The objective of this project is to determine the ability of present continuous wave Doppler ultrasound technology to non-invasively detect the presence of atheromatous plaques with particular emphasis on the carotid bifurcation. This will be performed by: (1) Real time spectral analysis on abnormal Doppler signals associated with plaques. (2) Performance of xeroradiography on carotid bifurcation of patients with asonic gaps in the Doppler arterial images to determine the correlation between the findings. (3) Recording Doppler signals and flow images along excised human arteries containing plaques and establish correlation between plaque geometry and composition and the abnormal Doppler signals. (4) Recording Dopper signals and flow images on dialysis tubing containing excised human carotid artery plaques and correlate the findings of the abnormal signals with the composition and geometry of the plaque material.